Renewable energy resources also include the energy of ocean waves, whose energy potential is estimated to be able to provide roughly 15% of worldwide power demand. Ocean waves inherently constitute a type of ocean movement which is less regular in terms of time and space, but no less energy-rich, such as, for example, the known motion of the tidal range.
The technical implementation for obtaining the energy from the ocean can be based on different principles. One possible implementation principle is based on a dual-mass system which floats in water. The two masses are used. As a result of the natural frequencies which are distinctly different from one another, the masses have different relative motions with respect to one another due to wave motion. These relative motions of the masses with respect to one another can be converted into pump motions of working cylinders, such as hydraulic cylinders, to then obtain, for example, by a generator, electrical energy. The hydraulic energy converts into usable current by the working cylinder, caused by mechanical energy in the form of wave motion.
DE 601 15 509 T2 discloses a pertinent, point-absorbing wave energy converting device for obtaining energy from wave motion on the surface of a body of liquid and with dimensions which are small compared to the wavelength of the predominant wave. The known solution has two devices which can move in relative terms opposite one another as two movable individual masses. The first device has a float. The second device has a submerged body underneath the surface of the body of liquid. Hydraulic working cylinders between these two mass devices execute lifting motions for energy transfer from mechanical into electrical energy due to the relative motion of the individual masses with respect to one another caused by the wave motion.
In these dual-mass systems which float in water, often a time offset is between the wave motion and the guided motion of at least one of the masses of the dual-mass system, with the result that mass motion can be stopped or at least decelerated. This time offset, for example, when the amplitude of the wave after passing through the wave trough rises again, while at least one of the two masses following in time is still in downward motion in the direction of the wave trough and then is slowed down or even stopped in this motion by the already rising wave. The energy conversion is adversely affected or even stopped by this “retarding moment.” To counteract these failure phenomena, PCT-WO 2005/069824 A2 describes an energy converting device which makes it possible, with inclusion of the corresponding sensor technology, to briefly switch over a generator for current generation, caused by the wave motion, and a corresponding mechanical converter segment in the form of a rack and pinion drive, into motor operation. At least some of the energy obtained beforehand can then be used again to drive a mass which has been set in the direction of standstill dictated by the wave motion, such that the indicated dead point phases are overcome. Depending on the actual circumstances of the wave motion, the energy converting device can then be used either as a generator in the energy recovery mode or in motor operation as a driving control force for the respective mass of the energy converting device to ensure a basic situation of motion from which the mass can be moved more easily by the wave than if it assumes a decelerated state or even a rest state. In spite of the energy yield which is improved in this way, however, for driving the mass out of the respective wave dead point zone, energy is lost again in the motor operation of the device. Overall, this loss reduces the possible energy yield.
The magnitude, height, and frequency of wave motion are highly variable, as are the absolute values of the magnitudes of motion as well as the pertinent relative value of the body excited by it in the form of the individual movable masses. Due to the variable behavior of the wave motion, in practice the conversion of the mechanical energy associated with it into electrical energy poses problems, in the sense that uniform current delivery is not achieved, and/or as a result of feedback processes the “mechanical wave machine” is stopped by the respective working cylinders being stopped or at least greatly decelerated in their motion.